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Endurance athletes commonly consume carbohydrate-electrolyte sports beverages during prolonged events. The benefits of this strategy are numerous—sports-beverage consumption during exercise can delay dehydration, maintain blood glucose levels, and potentially attenuate muscle glycogen depletion and central fatigue. Thus, it is generally agreed that carbohydrate-electrolyte beverages can improve endurance performance. A controversy has recently emerged regarding the potential role of protein in sports beverages. At least 3 recent studies have reported that carbohydrate-protein ingestion improves endurance performance to a greater extent than carbohydrate alone. In addition, carbohydrate-protein ingestion has been associated with reductions in markers of muscle damage and improved post exercise recovery. Although many of these muscle damage and recovery studies examined post exercise nutritional intake, recent evidence suggests that these benefits may be elicited with carbohydrate-protein consumption during exercise. These findings are intriguing and suggest that the importance of protein for endurance athletes has been underappreciated. However, 2 studies recently reported no differences in endurance performance between carbohydrate and carbohydrate-protein beverages. The varied outcomes may have been influenced by a number of methodological differences, including the amounts and types of carbohydrate or protein in the beverages, the exercise protocols, and the relative statistical power of the studies. In addition, although there are plausible mechanisms that could explain the ergogenic effects of carbohydrate-protein beverages, they remain relatively untested. This review examines the existing research regarding the efficacy of carbohydrate-protein consumption during endurance exercise. Limitations of the existing research are addressed, as well as potential areas for future study.

The authors investigated the effects of postexercise carbohydrate-protein-anti-oxidant (CHO+P+A) ingestion on plasma creatine kinase (CK), muscle soreness, and subsequent cross-country race performance. Twenty-three runners consumed 10 mL/kg body weight of CHO or CHO+P+A beverage immediately after each training session for 6 d before a cross-country race. After a 21-d washout period, subjects repeated the protocol with the alternate beverage. Post intervention CK (223.21 ± 160.71 U/L; 307.3 ± 312.9 U/L) and soreness (medians = 1.0, 2.0) were significantly lower after CHO+P+A intervention than after CHO, despite no differences in baseline measures. There were no overall differences in running performance after CHO and CHO+P+A interventions. There were, however, significant correlations between treatment differences and running mileage, with higher mileage runners having trends toward improved attenuations in CK and race performance after CHO+P+A intervention than lower mileage runners. We conclude that muscle damage incurred during training was attenuated with postexercise CHO+P+A ingestion, which could lead to performance improvements in high-mileage runners.

Carbohydrate–protein (CHO+Pro) beverages reportedly improve endurance and indices of muscle disruption, but it is unclear whether these effects are related to total energy intake or specific effects of protein.

Previous studies reported that adding protein (PRO) to carbohydrate (CHO) solutions enhances endurance performance. The ergogenic effect may be a function of additional protein/amino acid calories, but this has not been examined. In addition, although supplemental L-alanine (ALA) is readily oxidized during exercise, the subsequent impact on metabolism and prolonged endurance performance is unknown. The purpose of this investigation was to independently gauge the impact of whey PRO hydrolysate and ALA supplementation on performance and various physiological parameters. Eight cyclists (age: 22.3 ± 5.6 yr, weight: 70.0 ± 8.0 kg, VO_2max: 59.4 ± 4.9 ml·kg⁻¹·min⁻¹) performed 120 min of constant-load cycling (55% of peak power) followed by a 30-km time trial (TT) under placebo (PLA), PRO, and ALA conditions. Magnitude-based qualitative inferences were applied to evaluate treatment differences and data are presented as percent difference between treatments ± 90% confidence limit. Both ALA (–2.1 ± 2.7%) and PRO intake (–2.1 ± 2.2%) possibly harmed performance compared with PLA. Of interest, heart rate was possibly lower with ALA than PLA at 20– (–2.7 ± 3.4%) and 120-min (–1.7 ± 2.9%) of constant-load cycling and the serum interleukin-6 (IL-6) response to 120 min of cycling was likely attenuated with PRO compared with PLA (PLA, 6.6 ± 3.7 fold vs. PRO, 2.9 ± 1.8 fold). In addition, blood glucose levels were lower with PRO than PLA at 20– (–8.8 ± 2.3%; very likely) and 120-min (–4.9 ± 4.6%; likely) of constant-load cycling. Although ALA intake appears to lower HR and PRO ingestion dampens the IL-6 response to exercise, the ingestion of PRO (without CHO) or ALA does not enhance, and may actually impair, performance following prolonged cycling.

This study examined whether a carbohydrate + casein hydrolysate (CHO+ProH) beverage improved time-trial performance vs. a CHO beverage delivering ~60 g CHO/hr. Markers of muscle disruption and recovery were also assessed. Thirteen male cyclists (VO_2peak = 60.8 ± 1.6 ml · kg⁻¹ · min⁻¹) completed 2 computer-simulated 60-km time trials consisting of 3 laps of a 20-km course concluding with a 5-km climb (~5% grade). Participants consumed 200 ml of CHO (6%) or CHO+ProH beverage (6% + 1.8% protein hydrolysate) every 5 km and 500 ml of beverage immediately postexercise. Beverage treatments were administered using a randomly counterbalanced, double-blind design. Plasma creatine phosphokinase (CK) and muscle-soreness ratings were assessed immediately before and 24 hr after cycling. Mean 60-km times were 134.4 ± 4.6 and 135.0 ± 4.0 min for CHO+ProH and CHO beverages, respectively. All time differences between treatments occurred during the final lap, with protein hydrolysate ingestion explaining a significant (p < .05) proportion of betweentrials differences over the final 20 km (44.3 ± 1.6, 45.0 ± 1.6 min) and final 5 km (16.5 ± 0.6, 16.9 ± 0.6 min). Plasma CK levels and muscle-soreness ratings increased significantly after the CHO trial (161 ± 53, 399 ± 175 U/L; 15.8 ± 5.1, 37.6 ± 5.7 mm) but not the CHO+ProH trial (115 ± 21, 262 ± 88 U/L; 20.9 ± 5.3, 32.2 ± 7.1 mm). Late-exercise time-trial performance was enhanced with CHO+ProH beverage ingestion compared with a beverage containing CHO provided at maximal exogenous oxidation rates during exercise. CHO+ProH ingestion also prevented increases in plasma CK and muscle soreness after exercise.